I took a hole saw that was old...you can use a pipe or whatever. Just make sure the "inside diameter" is the size you need your inserts to be.
then take a grinder or file and bevel the edge to make it sharpish.
Place the punch that you just made on the neoprene and give it a whack with a hammer.
instant insert blank.
One floor mat yielded aprox. 150 inserts for me (mine are 1.5")
total cost was 12 bucks for (not including diy punch) enough material to make 600 inserts.
Super bonus for guys who do not re-use their inserts (I do though)
All that is left is to put a slit into them with a razor blade or scissors. I found that scissors made a great cut.
Compare this to ebay insert prices!!!!
any questions go ahead and ask away